Cyclizine is a histamine H₁receptor antagonist.^1,2,3It binds selectively to histamine H₁receptors (K_d= 5 nM) over H₂and H₃receptors (K_ds = 1,600 and >580 nM, respectively).³Cyclizine inhibits anti-IgE-induced histamine release from isolated human lung fragments with an IC₅₀value of 5.42 ?M but induces histamine release with a 50% release concentration (RC₅₀) of 10.81 ?M.⁴It reduces LPS-induced nitrite accumulation and protein levels of induced nitric oxide synthase (iNOS) in RAW 264.7 cells when used at a concentration of 100 nM.²Cyclizine (10 and 20 mg/kg) reduces immobility in the forced swim test in rats.⁵

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